94boosted

Just recently I've noticed that I'm filling up my 2010 GS more than I ever used to. I checked the mileage on the highway recently and I averaged 24.5MPG, this was on a warm (not hot), not windy day at 80MPH with cruise control on during a ~60 mile drive. Shouldn't I be around 28-31MPG?

The car has 16K Miles and is mildly modified (headers, intake & custom diablew tune). It's well maintained (oil changes every 3K miles) and I put new plugs in about a year ago. Tire pressure are correctly set. Any thoughts? Should I run fuel system cleaner like STP through the system (that's never been done)? Should I have my tuner re-check the tune?

Thanks in advance.

94boosted

I thought I'd mention that I did recently switch to a slightly more aggressive alignment:

Performance Street - Track Use with Race Tires
Front min max
Camber (deg) -1.6 -1.8
Caster (deg) 7.5 8.5
Total Toe -1/16" (0.17°) 0 (0°)
Rear
Camber (deg) -0.9 -1.1
Total Toe -1/8" (0.33°) -1/16" (0.17°)

Kent1999

80 is pretty fast for max mileage. Your observed MPG of about 25 seems roughly in line for that speed.

I can knock down 27 mpg avg if I am careful and go about 70-75 in my unmodified GS manual. But I *do* notice I get less MPG in the hotter summer months -- maybe you are seeing the same thing?

94boosted

It was between 74-81MPH, but for the most part 80. It was summer yes but that day it was only 60°F.

WA 2 FST

Granted my car has more mods than yours, but I just got back from a 500 mile round trip (90% highway) and got 24... doing 80, with some start/stops on some more rural state highways. I was pleased. Mine is an A6 car.

94boosted

haha I'd say yours is significantly more modded than mine.

Joe_G

I think your mileage is right in line. If you slow down 10 mph it'll go up more than you think. I learned that hypermiling my Prius - speed really affects mileage.

Not that I'm suggesting your slow down - just be happy that you have an affordable super car that gets 25 mpg!

Z0HS1CK

I picked up almost 1 MPG after currently switching to long tubes, catless xpipe and a aftermarket axleback.

Now i'm at 21.5 or something. When i do drive the car, on the weekends, its a combination of both city and highway but i try to hit the highway more.

ParisTNDude

Gees, I thought mine was running poorly when it dropped o 26 mpg in the early spring on the high way. I got more than a couple of tanks at better than 28 during my early summer trip to Texas and back this year running 70-75 or so.

I also have a 2010 GS with 17k miles on it and a 6M. I thought running the AC would drop the mpg by a couple, but it didn't seem to effect the MPG at all. I have only a CAI and a Diablo tune on mine.

94boosted

Thanks for all the feedback folks

Just for fun I'm going to set cruise at 70MPH and see if I can get 28MPG.

Guard Dad

I never see anything above 25 mpg. I've got an 11 GS M6 stock. The AC is on most of the time because it's California and it's hot most of the time. The trip I'm thinking of was a 1,200 mile sight seeing tour to Northern California and back. The traffic was light and the speeds were mixed but never above 75 and no aggressive driving because the wifey does not like it if I get sporty with her in the car. To me your mileage sounds about right. I had a 99 Camaro SS with a similar power train and the only time I ever got 27-28 mpg was on straight shots up the I-5 to the Bay Area at 75 on cruise but the moment I hit anything like traffic the mileage would begin to fall back to about 24 mpg. For city driving both the SS and GS were/are in the mid to high teens.

GSDriver

Also look to see if your pump fuel has ethanol in it. It will get less mileage.

AIR_RAM

I get 12MPG in mine... It just went up from 10MPG to 12MPG since I'm not WOT as often... I don't think I have ever seen above 20MPG... But I'm not really trying to get good MPG.

Check the obvious... tire pressure, fuel condition... if you don't drive much it may take a tank or two of fresh fuel to dilute and burn the older fuel. Drive it till its on fumes and then fill it up with top tear gas.

Slowing down will ALWAYS improve MPG... You WILL see better fuel economy at 40MPH than you will at 80MPH... Its up to you to determine if the speed is worth the price of the fuel your burning.

Also, remember every time you go WOT, any chance of decent MPG in that tank are GONE! Once WOT blast will kill any MPG gains made with that tank... You will not be able to make up for it in the end. So if MPG is your goal... do not go WOT.

The important thing is that you enjoy the ride! If your happy at 80MPH, then just accept the 24MPG which is about right on par with that speed.

SPEED SAFE, AIR RAM

94boosted

Slowed down a bit and cruised at 120km/h (74MPH) and mileage went up a bit to 25.6MPG. Will try cruising at 110km/h (68MPH) and see how that affects mileage. AC was on for some but not all of the time, cruise control was also on, weather was 68*F.

It still seems a bit high to me but from the posts above maybe not. Oh and I'm not sure altitudes effect on mileage but we are at 3600 feet above sea level.